It is difficult to give any complete idea of the activity maintained at the Newark shops during these anxious, harassed years, but the statement that at one time no fewer than forty-five different inventions were being worked upon, will furnish some notion of the incandescent activity of the inventor and his assistants. The hours were literally endless; and upon one occasion, when the order was in hand for a large quantity of stock tickers, Edison locked his men in until the job had been finished of making the machine perfect, and "all the bugs taken out," which meant sixty hours of unintermitted struggle with the difficulties. Nor were the problems and inventions all connected with telegraphy. On the contrary, Edison's mind welcomed almost any new suggestion as a relief from the regular work in hand. Thus: "Toward the latter part of 1875, in the Newark shop, I invented a device for multiplying copies of letters, which I sold to Mr. A. B. Dick, of Chicago, and in the years since it has been universally introduced throughout the world. It is called the 'Mimeograph.' I also invented devices for and introduced paraffin paper, now used universally for wrapping up candy, etc." The mimeograph employs a pointed stylus, used as in writing with a lead-pencil, which is moved over a kind of tough prepared paper placed on a finely grooved steel plate. The writing is thus traced by means of a series of minute perforations in the sheet, from which, as a stencil, hundreds of copies can be made. Such stencils can be prepared on typewriters. Edison elaborated this principle in two other forms--one pneumatic and one electric--the latter being in essence a reciprocating motor. Inside the barrel of the electric pen a little plunger, carrying the stylus, travels to and fro at a very high rate of speed, due to the attraction and repulsion of the solenoid coils of wire surrounding it; and as the hand of the writer guides it the pen thus makes its record in a series of very minute perforations in the paper. The current from a small battery suffices to energize the pen, and with the stencil thus made hundreds of copies of the document can be furnished. As a matter of fact, as many as three thousand copies have been made from a single mimeographic stencil of this character. CHAPTER IX THE TELEPHONE, MOTOGRAPH, AND MICROPHONE